1. Field of the Invention
The present invention relates to a downhole tool. More particularly, the invention relates to a downhole tool that can be actuated in multiple, separate ways. More particularly still, the invention relates to a downhole anchor that can be set either mechanically or hydraulically in casing of a variety of sizes and weights.
2. Description of the Related Art
When oil and gas wells are drilled, a bore hole is formed in the earth and typically lined with steel pipe that is cemented into place to prevent cave in and to facilitate the isolation of certain areas of the wellbore for the collection of hydrocarbons. Once the steel pipe or casing is cemented into place, the hydrocarbons are typically gathered using a smaller string of tubulars, called production tubing. Due to a variety of issues, including depletion of formations adjacent the wellbore and stuck tools and pipe that prevent continued use of the wellbore, it is often desirable to form another wellbore, not from the surface but from some location along the existing wellbore. This new, or lateral wellbore can be lined with pipe and hydrocarbons can then be collected along its length. It is not uncommon to have more than one lateral, or sidetracked wellbore extending from a single central or parent wellbore.
Initiating a new wellbore from a cased, central wellbore requires a hole or window be formed in the casing wall adjacent that location where the new wellbore will commence. Forming windows is typically done with the help of a whipstock which is a wedge-shaped member having a concave face that can “steer” a mill or cutter to a side of the casing where the window will be formed. Whipstocks and their use are well known and an example is shown in U.S. Pat. No. 6,464,002 owned by the same assignee as the present invention and that patent is incorporated by reference herein in its entirety. The whipstock may be run in by itself or to save a trip, the whipstock might be run in with the mill or cutter temporarily attached to its upper edge. In any case, the whipstock has to be anchored in the wellbore at its lower end to keep it in place and to resist the downward force placed upon it as the cutter moves along its length through the casing wall.
Various anchors are used with whipstocks and prior art anchors can be mechanically set or hydraulically set. Mechanical anchors include those that require a compressive force to shear a pin and permit the anchor to assume a second, set position. Mechanical anchors work well when the anchor is to be set at the bottom of a wellbore or when there is some type of restriction that has been placed in the wellbore, like a bridge plug. In those instances, there is a stationary surface available to use to generate the compressive force needed to set the mechanical anchor. In other instances, the anchor must be set at some point along the wellbore where there is no surface to act upon in order to create a compressive force. In these instances, the anchors can be set with pressurized fluid, but that requires a different apparatus and the type of anchor actually needed on a job is not always apparent in advance.
Because of the uncertainty of equipment needed to best form a window in a casing, there are instances in which the wrong type anchor is on site and delays are created as another more appropriate anchor is found. An additional problem relates to the fact that most prior art anchors offer little flexibility in the size casing in which they can operate. For example, prior art anchors with slip and cone arrangements are designed to increase their outer diameters minimally when they are set and only work properly when they are designed for the specific inner diameter casing in which they are used. Additionally, it is not uncommon to encounter a restriction in the form of garbage as even casing of a smaller inside diameter prior to reaching larger diameter casing where the anchor is to be set. Many prior art anchors that are small enough to fit through the restriction will not expand far enough to become properly set in the larger casing.
There is a need for an anchor that is adaptable to be operated either mechanically or hydraulically. There is a further need for an anchor that can be operated in casings of varying diameters.